Formation of the adakite-like granitoid complex and porphyry copper-gold deposit in Shaxi from southern Tancheng-Lujiang fault belt: A clue to the West Pacific plate subduction

Abstract

On the basis of the geological and geochemical studies, including chemical analysis of bulk rocks, rare-earth and trace element studies, fluid inclusion, and S and O isotopic analyses, the authors described the geological background of the deposit in detail and presented significant proofs for the conditions of formation of the Shaxi porphyry copper-gold deposit. Compared with other large and supper-large porphyry copper deposits in China and the adjacent Cu-Au mineralized areas, the ore-forming processes and conditions were analyzed; and the possibility of forming large porphyry copper deposits in the Shaxi area was discussed. The present study indicated that the ore-forming fluid and material were mainly of magmatic origin, while meteoric water played a certain role in the ore-forming processes. Interactions between subducting and overriding plates provided a major driving force for the formation of igneous rocks and the deposition of metal elements in East China since Jurassic. Based on the geochemical data of the Shaxi intrusive, it is found that the copper (gold) mineralization is closely related to the genesis of adakite-like intrusive in the Shaxi area. This adakite-like intrusive was formed in the subduction environment as a result of the subduction of the West Pacific plate toward the East China continent, where there is a great potentiality to form a large porphyry copper deposit.

A review of the intracontinental porphyry deposits in the Middle-Lower Yangtze River Valley metallogenic belt, Eastern China

“…Post-127 Ma, when regional extension Zhao et al (1985), Meng and Huang. (1988), Huang et al (1990), Lv et al (1992), Zhang (1992), Fu et al (1996), Lan et al (2009), Xu et al (2011), Fang (2012 and our unpublished data. reached a peak.…”

“…The potassic-, phyllic-and propylitic alterations took place in the temperature range of 450-340°C, 340-250°C and 250-170°C, respectively, and ore fluids were mainly enriched in H 2 O and SO 2 (our unpublished data). δ 34 S values of pyrite and chalcopyrite are − 0.2-3‰ and − 0.3-1.3‰ (Fu et al, 1996;Lan et al, 2009), respectively, suggesting a magmatic source. δ 18 O and δD of the ore fluids are + 0.4 to + 5.5 ‰ and − 60 to − 84 ‰, respectively, indicating a largely magmatic constituent with minor involvement of meteoric water (Fu et al, 1996;Lan et al, 2009).…”